The invention relates to a process for the production of ketones unsaturated in the alpha, beta position to the carbonyl group by reacting an aldehyde with a ketone in the presence of a catalyst consisting essentially of either of zinc acetate or zinc acetate dihydrate.
The use of zinc acetate in carrying out such reactions has heretofore been unknown and is not obvious from the teachings of the prior art. Thus, Houben-Weyl, "Methoden der Organischen Chemie", volume 7/1, pages 77 et. seq. and "Organic Reactions", volume 16, pages 27 to 47, 69 to 78 and 177 et seq. disclose the fact that aldehydes and ketones can be converted to alpha, beta unsaturated ketones. Temperatures of from 5.degree. C. up to 100.degree. C. are preferred for this aldol condensation ("Organic Reactions," loc. cit., page 77). The numerous catalysts used in these methods, for example alkali and alkaline earth metal hydroxides, organic bases, alkali metal salts and alcoholates promote auto-condensation of the aldehydes and ketones and therefore causes the formation of large amounts of by-products in most cases.
Furthermore, the U.S. Pat. No. 4,005,147 discloses the production of alpha, beta unsaturated ketones by reacting in the liquid phase an aldehyde with a ketone in the presence of a catalyst consisting essentially of zinc oxide.
It is furthermore known from U.S. Pat. No. 2,549,508 that aldehydes and ketones can be converted into unsaturated ketones of high molecular weight in the gas phase at temperatures of from 500.degree. to 1000.degree. C. in the presence of a catalyst consisting essentially of zinc oxide and from 1 to 15% by weight of zirconium oxide. In this process, however, only low conversions and low yields are achieved. Moreover high expenditure for equipment is required for reactions in the presence of hydrogen at the said temperatures for safety reasons. Moreover cracking processes take place at the surface of the catalyst in such reactions and these have a negative effect on the life of the catalyst.
The reaction of two identical or different aldehydes or ketones in the liquid phase at elevated temperature and in the presence of a catalyst (obtained by calcining a mixture of molybdenum oxide, magnesium oxide with or without zinc oxide or compounds of these metals) to form alpha, beta-unsaturated aldehydes or ketones is known from German Pat. No. 1,203,243.
According to the method described in the said patent good conversions and very good yields of alpha, beta-unsaturated aldehydes are obtained in the condensation of aldehydes with one another, particularly, in the condensation of n-butyraldehyde or 2-ethylhexenal.
The process of German Pat. No. 1,203,243 is not so suitable for the reaction of aldehydes with ketones to form alpha, beta-unsaturated ketones, considerably lower conversions and selectivities being achieved. This is particularly noticeable when not only isobutyraldehyde (i.e., and aldehyde which does not undergo autocondensation) is reacted with a ketone by the method of the said German patent, but also when aldehydes are used which readily undergo autocondensation, as for example 3,3-dimethylacrolein and citral.
Nothing in the prior art however implies the process of our invention using either a zinc acetate catalyst or a zinc acetate dihydrate catalyst whereby certain ketones may be produced in a convenient, sufficient and economical manner.